1. Field of the Invention
The present invention relates to an ultrasonic motor and a manufacturing method thereof.
2. Description of the Related Art
An ultrasonic motor is a kind of small actuator that can be used for mechanical driving components within various electronic devices, such as components within a cellular phone, a digital camera, a Personal Data Assistant (PDA), a camera for a notebook, etc. Specifically, an ultrasonic motor may be used for auto focus (hereinafter, referred to as “AF”), Optical Image Stabilization (OIS), zoom, a shutter, etc.
A piezoelectric ultrasonic motor may be designed, develop, and manufactured in consideration of a variety of factors, including miniaturization, operation stability, guarantee of reliability, mass producibility, etc.
Actuators within ultrasonic motors are largely divided into two types. A first type of actuators uses electromagnetism. This first type of actuators includes motors using an electromagnetic force between a magnet and a coil, such as a voice coil motor, a step motor, etc. A second type of actuators uses a piezoelectric material. This second type of actuators uses a piezoelectric material that generates mechanical displacement through an electric field, or generates voltage by mechanical deformation. In other words, the second type of actuator drives by causing a mechanical change in the piezoelectric material through application of an electric source to the piezoelectric material, and generating a frictional force with a contact portion through application of a mechanical pressure from the outside. Such an actuator may include a Longitudinal or Bending Mode (L1B2) ultrasonic motor, a Smooth Impact Drive Mechanism (SIDM), and the like. There are also various other kinds/types of piezoelectric actuators using a cantilever, or similar elements.
However, the first type of actuator using electromagnetism has several problems because, this type uses an electromagnetic force between a magnet and a coil. Therefore, a large amount of power is consumed by the motor itself. The first type of actuator is also difficult miniaturize, has a low resolution, generates an electromagnetic field, and has no holding torque for maintaining a position when the actuator is stopped. Thus, for the motor and a controller, continuous driving and power consumption are required to maintain a lens position when the actuator is used for AF of a camera of a mobile terminal, or other similar functions. This may be a significant disadvantage in a mobile device. Also, there is a problem of reproducibility. Specifically, a change in a load amount is caused by gravity when the direction of a mobile terminal is turned, which causes a problem of the reproducibility of the motor.
By contrast, the second type of actuators using a piezoelectric material is superior to the first type of actuator using electromagnetism in regards to power consumption, size, resolution, generation of an electromagnetic field, etc. However improvements in regards to miniaturization, reliability, stability, mass producibility, a price, etc. are still desired, even for the second type of actuators.
FIG. 1 is a view showing the external structure of a conventional L1B2 mode ultrasonic motor.
A conventional L1B2 mode ultrasonic motor requires, at a lower end thereof, a groove and an inactive section for seating a contact tip, and further requires, at an upper end thereof, another inactive section with the same thickness as that the thickness of the inactive section at the lower end to minimize L1 B2 mode distortion. This causes an increase in the entire thickness of the motor, thereby hindering miniaturization of the motor. The inactive sections at the upper/lower ends also reduce displacement, thereby reducing the performance of the motor. In other words, the inactive section at the lower end is necessary to stably seat a contact material, and also the inactive section at the upper end, which is symmetrical to that at the lower end, is necessary to avoid mode distortion. These inactive sections at the upper/lower ends cause an unfavorable effect on the miniaturization and the performance.